An Overview of 802.11a and 802.11b Products

By now, we're all familiar with 802.11b wireless networking. But
there's also been lots of discussion recently about two other wireless
standards, both of which are in the 802.11 family: 802.11a and
802.11g.

802.11g is still in the process of being finalized and is currently in
draft specification. However, a few vendors are already marketing new
802.11g devices. In terms of availability, however, 802.11a products are
more plentiful than 802.11g. In this article, I'll provide an overview of
802.11a and 802.11b devices that are currently available, and I'll share
some of my compatibility tests on these devices to help you make informed
decisions when adding to your WiFi network.

Comparing 802.11a and 802.11b

Before we take a look at the various WiFi products, let's compare some
basic characteristics of 802.11a and 802.11b by looking at a few
parameters:

Frequency - 802.11b uses the 2.4 Ghz spectrum, which is overcrowded
with devices like cordless phones and microwave ovens. Even Bluetooth
devices use the 2.4Ghz spectrum. 802.11a, on the other hand, uses the less
crowded 5Ghz spectrum. Though the 5Ghz spectrum is less crowded, the
signals have higher absorption rate and this causes it to be easily
blocked by walls and objects.

Range - Due to the higher absorption rate at the 5Ghz spectrum,
802.11a devices have shorter operating range of about 150 feet, compared
to the 300 feet achievable by 802.11b (optimally under ideal
conditions). As a result, more transmitters are required for 802.11a
networks.

Data rate - 802.11a supports speeds up to 54Mbps, while 802.11b
supports speeds of up to 11Mbps.

Cost - Components for 802.11a devices are more expensive to produce
and hence their price tags are higher than 802.11b devices. Also, the
increased number of transmitters required for 802.11a network will drive
up the cost of implementing an 802.11a network.

Compatibility - 802.11a is not compatible with the 802.11b
protocol. Hence 802.11a devices cannot work with existing 802.11b wireless
access points. Note that if you plan on migrating to the newer 802.11g
standard, your 802.11b cards can access the "g" network. This will not be
the case for 802.11a radio cards.

Users - 802.11a network can accommodate more users due to the increase
in radio frequency channels and increased operating bandwidth.

The main draw of migrating to an 802.11a network is no doubt increased
bandwidth. With the near five-fold increase in data rate (54Mbps),
applications like audio and video streaming and networking games would be
possible (or at least more responsive).

However, the drawback in adopting 802.11a is compatibility. Businesses
and institutions that have invested in 802.11b networks are reluctant to
migrate to a faster, but incompatible 802.11a network. For these reasons,
vendors are coming out with dual-band wireless points. These dual-band
access points support both 802.11a and 802.11b devices. You can deploy
both 802.11a and 802.11b devices all in the same environment. Best of all,
since these two protocols are operating in different frequencies,
interference is minimized.

The following table shows some of the 802.11a and 802.11b devices
available in the market:

Testing the Products

I've managed to obtain evaluation units from two major vendors: Linksys and D-Link. For my test I'm primarily
interested in comparing the data rates of the two 802.11 standards. I am
also interested to know how compatible these devices are when I mix and
match access points and adapters.

To test the raw speed of the devices, I setup a web server to serve a
624MB movie file. The wireless device will download the file and I want
to see the effective download speed. I did not test the Internet access
speed as too many factors can skew the results (such as network delays
and server overloading). I placed the wireless client and the access
point within the same room.

Presented below are the various configurations and their acquired
data rates:

Wireless Access Point(s)

Wireless Clients

Data Rate

Linksys BEFW11S4

Linksys WPC11

528KB/s

This is a pure 802.11b network since
both access point and client using 802.11b.

Linksys BEFW11S4

D-Link DWL-650+ AirPlus

546KB/s

I am using a normal Linksys access point
with the D-Link Airplus 802.11b card. The data rate is comparable to the previous
one.

D-Link DI-714P+ AirPlus

D-Link DWL-650+ AirPlus

723KB/s

I am using D-Link AirPlus products - access point and network card. The
data rate is significantly higher since both are AirPlus products, which supports
a faster data rate. Still, this is an 802.11b network.

Linksys BEFW11S4 connects to D-Link DWL-6000AP AirPro

D-Link DWL-650+ AirPlus

729KB/s

I connect my Linksys wireless access point (with router) to the D-Link
multimode access point, which supports 802.11a and 802.11b. However my network
card is still 802.11b. The improved performance (over standard 802.11b) is due
to the AirPlus feature.

Linksys BEFW11S4 connects to
Linksys WAP51AB

D-Link DWL-AB520 AirPro

1.11MB/s to 2.89 MB/s

I connect my Linksys
wireless access point (with router) to the Linksys WAP51AB, which supports both
802.11a and 802.11b. On the client side, I use the D-Link PCI wireless point,
which also supports both 802.11a and 802.11b. I obtained a data rate ranging from
1.11MBps to 2.80MBps.

Figure 1. Stacking up the two Linksys wireless access points

Linksys BEFW11S4 connects to Linksys WAP51AB

Linksys WPC51AB

1.11MB/s to 2.89 MB/s

I connect my Linksys wireless access point (with
router) to the Linksys WAP51AB, which supports both 802.11a and 802.11b. On the
client side, I use the Linksys wireless card, which supports only 802.11a. I obtained
a data rate ranging from 1.11MBps to 2.80MBps.

Let's take a look at the numbers. For an 802.11b network, I have
consistently achieved a data rate of 528KBps. This translates to 528*8
(bits) Kbps=4224 Kbps=4.125Mbps. Compare this to the advertised rate of
11Mbps; you can see that the effective data rate is actually much
lower.

Even for products that use proprietary techniques to boost speed (such
as the D-Link's 802.11b AirPlus), the figures are just slightly
better. 729KBps=5.7Mbps. And this is the effective data rate for
AirPlus's 22Mbps products.

The chart in Figure 2 summarizes the comparative performance of 802.11a
and 802.11b devices.

Figure 2. Comparing performances of 802.11

Summary

Is this the time for you to jump onto the 802.11a bandwagon? From the
perspective of pure data rate, the answer is a definite yes. But if you
have an existing wireless network utilizing 802.11b devices and access
points, you have to consider the cost of upgrading all devices to
802.11a. However, an easy way out would be to consider a dual mode access
point, which can support both 802.11a and 802.11b devices.

If time is on your side, I suggest you wait for the newer 802.11g
standard to stabilize. 802.11g delivers the same performance as 802.11a
but is compatible with 802.11b devices and thus preserves your investment
on current technology. Vendors are already beginning to sell 802.11g
devices based on the draft specification. I will talk more about 802.11g
devices as they become more widely available in the market.